1. Technical Field
The invention relates to a direct current (DC)-to-DC control technique. Particularly, the invention relates to a DC-DC controller and a multi-ramp signal operating method thereof.
2. Related Art
Referring to FIG. 1, in a circuit structure with constant on time (COT), a single ramp signal RAMP is generally intersected with and compared with an error signal COMP to generate an on time signal PWM_Ton. When the on time signal PWM_Ton used for pulse width modulation is started to be calculated, the ramp signal RAMP is immediately reset and recharged to a vertex of a voltage level thereof. It has to spend a constant time Ramp_Tc for charging the ramp signal RAMP. However, along with variation of a frequency of the circuit structure or phase switching of multi-phase, the constant time Ramp_Tc is bound to occupy a considerable time on a cycle of the ramp signal RAMP. For example, it is assumed that the originally required constant time Ramp_Tc is 100 μs, when the frequency is increased to change the cycle of the ramp signal RAMP to 50 μs, a transient response phenomenon is occurred due to inadequate charging time, which probably causes phase instability.